Generally, an inductor is one component constituting a circuit for Radio Frequency (RF) transmission/reception, and is essentially used in RF devices and analog devices, which have been widely used with the expansion of the wireless communication market. An inductor is generally formed in a spiral structure. Such an inductor having a spiral structure is disadvantageous in that the self-resonant frequency thereof decreases due to parasitic capacitance between the metal wires of the inductor.
Generally, the transition frequency point of an inductor at which the input impedance of the inductor changes from inductance to capacitance as the frequency increases is referred to as a self-resonant frequency. An inductor is mainly used at a frequency lower than the self-resonant frequency. In the case of an inductor having a spiral configuration, as the inductance value of a device increases, the size of the device increases and a parasitic component also increases so that the self-resonant frequency of the inductor decreases. This results in an actual reduction of a usable frequency band.
Hereinafter, a conventional inductor is described with reference to the drawings. FIG. 1A is a plan view showing a conventional inductor, and FIG. 1B is a sectional view taken along line A-A of FIG. 1A.
Referring to FIGS. 1A and 1B, an interlayer dielectric 11 is formed on the top of a silicon substrate 10, and is then planarized. Thereafter, an inductor metal wire 12 having a spiral structure is formed on the interlayer dielectric 11. The inductor metal wire 12 is connected to a lower metal wire 12, through a via (not shown). An upper protective film 13 is formed on the inductor metal wire 12.
The parasitic capacitance of the inductor having a spiral structure increases as the interval (a) between the inductor metal wires 12 is narrowed, which results in the decrease in the self-resonant frequency and, also the reduction in the usable frequency band of the inductor accordingly.